HDD Technology and Equipment
A basic horizontal-directional drill-rig is illustrated in Figure 3-1. Horizontal directional drilling is accomplished using a drill rig. It services a bottom-hole assembly BHA that is responsible for creating a curved bore hole. The BHA consists of a drilling tool that is capable of creating a curved bore hole and a guidance system that locates the bore hole and directs changes in the trajectory. There is a variety of HDD rigs currently in use. Table 1-3 lists the three general categories of...
Chapter Footnotes 1
1 Geotechnical Engineers Handbook, Robert W. Day, McGraw-Hill, 2000 2 Horizontal Directional Drilling, Good Practices Guidelines, HDD Consortium, May 2001 3 J. D. Hair amp Associates, Louis J. Capozzoli amp Associates, and Stress Engineering Services 1995 . Installation of Pipelines by Horizontal Directional Drilling, An Engineering Design Guide, prepared for the Offshore and Onshore Design Applications Supervisory Committee of the Pipeline Research Committee.
Applications
HDD is a multi-billion-dollar annual industry with hundreds of contractors and thousands of drilling rigs operating on five continents. HDD in North America has grown from 12 operational units in 1984 to thousands of units today. This rapid growth is attributed at least partially to 1. The increasing traffic-control and restoration costs involved in the installation of utility conduits and pipes in congested urban areas and the need to dig around existing utilities. 2. The increased awareness...
Permitting and Easements
As in traditional pipeline or utility construction projects, there are numerous federal, state, and local agencies that may be involved in HDD crossings. Large projects or projects on federal land typically require a lead agency to coordinate the permit-application process and to monitor construction compliance with the applicable permits. The U.S, Bureau of Land Management, U.S. Forest Service, U.S. Fish and Wildlife, U.S. Army Corps of Engineers, and the Federal Energy Regulatory Commission...
Economic Feasibility
Once the technical feasibility of a prospective HDD installation has been established, its economic feasibility can be assessed. This assessment includes estimating the economics or costs of the HDD project as well as considering how the technical aspects of the project may impact project bids and contracts. This assessment can be accomplished by comparing it to the costs of past similar installations or by getting estimates or preliminary bids from qualified HDD contractors. HDD crossings that...
Breakaway Pulling Heads
Recent reports from several natural-gas utility companies reveal concerns regarding failure experiences on HDPE pipes installed by horizontal directional drilling. These failures were attributed to deformation of the pipe due to the use of excessive pulling force during installation. A mitigation measure adopted by some gas companies involves the use of breakaway swivels to limit the amount of force used when pulling PE products. The weak link used can be either a small-diameter pipe but same...
Drilling and Steering
Drilling curved and horizontal bore holes requires specialized drilling equipment. This equipment is contained in a bottom-hole assembly BHA that consists of a drilling tool, a bent subassembly, and a steering tracking tool. Pilot-hole directional control is achieved by using a nonrotating drill string with an asymmetrical leading edge. The asymmetry of the leading edge results in a steering bias. When a change of direction is required, the drill string is rotated so that the direction of the...
If
Torque Reamer duct and nuts and bolts passed through a pull chain. This put the entire load of the pull on the holes drilled through the duct and was for that reason quite ineffective. Today, every duct manufacturer recommends the use of a puller that distributes the load around the entire circumference of the duct. The most common type of puller has a set of wedge-shaped teeth on a conical mandrel that is inserted inside the end of the duct. As the mandrel is pulled forward, it forces the...
Distribution of Particle Sizes
The distribution of particle sizes larger then 0.075 mm No. 200 sieve is determined by sieving, while the distribution of smaller particle sizes is determined by a sedimentation process. For the USCS, rock fragments or soil particles are defined as follows 1. Boulders particles of rock that will not pass a 12-inch-square opening. 2. Cobbles particles of rock that will pass a 12-inch-square opening and be retained on a 3-inch U.S. standard sieve. 3. Gravel particles of rock that will pass a...
Equipment Setup and Site Layout
The following are guidelines for setting up equipment on the site 1. Sufficient space is required on the rig side to safely set up and operate the equipment. The workspace required depends on the type of rig used. A working space of similar dimensions to that on the rig side should be allocated on the pipe side, in case you need to move the rig and attempt drilling from this end of the crossing. 2. If at all possible the crossing should be planned to ensure that drilling proceeds downhill,...
Required Workspace
While selecting a larger class of drill rig may seem appropriate, you need to consider the available workspace as well as operating costs. The proper method is to balance the required power, pullback, torque, and fluid handling capacity with the drill rig that can do the HDD crossing reliably. The rig should be capable of doing most of the anticipated jobs without reaching the limits of the drill system's capabilities. The best drill system will perform the job while staying well within its...
DownHole Mud Motors
With high-capacity pumps and HDD rigs with higher drilling-fluid-flow capacities, the down-hole mud motor has become the tool of choice for directionally drilling in rock. The drilling-fluid requirements to power mud motors are much higher than for mixing and transporting cuttings however, the majority of the fluid can be recycled and reused. The important factors in classifying mud motors for HDD applications are the output torque, fluid volume requirements, and length. Length is important...
Project Contract Documents Plans and Specifications
The contract is important for all HDD projects. It is important that HDD contractors understand the project contract documents and technical specifications before starting any work. This will help reduce unexpected risks and delays in the project. It is very difficult to identify all the potential risks during the planning and design phase of any HDD project. The contract documents should address the risks of a failed bore due to unforeseen problems, and a shared-risk contingency plan should be...
General Information 1
When planning HDD crossings with plastic pipe, the primary concern for owners is usually whether the product pipe can safely handle the stresses and the required pullback loads. As discussed in Chapter 4, after selecting the required DR for the product pipe the next step is to determine if the DR selected can handle the installation loads. As with steel product pipe, plastic pipe, when installed by HDD, may experience high-tension loads, severe bending, and external fluid pressures. Usually...
FIGURE Typical HDD Drill Rig
must be anchored to provide a reaction against which the mechanical system can operate. Anchoring is typically done by driving stakes through openings at the front of the rig, attaching the rig to a buried weight, or simply attaching the rig to a large, heavy piece of equipment on the surface. The drill rig must provide sufficient thrust and the drill pipe sufficient strength to advance the drill string the full length of the proposed bore hole and sufficient pulling force to retract casing...
Rock Conditions
Factors that are used to determine the condition of rock are measurements of unit weight, hardness, and in situ conditions. Rock hardness has been correlated with the unconfined compressive strength of rock specimens. Table 2-31 lists the hardness of rock as a function of the unconfined compressive strength. Because the unconfined compressive strength is performed on small rock specimens, it often does not represent the actual condition of in situ rock. This is caused by the presence of joints,...
HDD Design Basics
The planning, design, and construction of HDD projects requires a specialized knowledge of pipeline construction methods and HDD equipment and technology. While Chapter 3 provides information about HDD equipment, this chapter discusses HDD design and installation. The planning and design of a HDD crossing should focus on meeting the requirements of the owner while keeping the project costs as low as possible. Many factors have an impact on HDD costs, but the most important is the crossing...
BorePath Profile
The procedures for designing the bore path for plastic pipe are basically the same as discussed for steel pipe in Chapter 6. The first step in calculating the estimated pulling loads is to develop the input data, such as pipe properties, DR, drilling-fluid properties, and code design factors, that will be used in the calculations. Examples of typically required input data are provided in the examples in this chapter. The bore path is selected based on the profile required to successfully cross...
Pulling Load Calculation
D 6.625in Pipe outside diameter, inches t ,219in Pipe wall thickness, Inches SMYS 42000psi Specified yield strength of pipe, psi SMYScode codedesign factor- SMYS SMYS 42000psi Average coefficient of frictbn between pipe and soil. Recommended value between .21 -.3 Maidla Fluid drag coefficient for steel tube pulled through bentonite mud Mud weight value. 12 ppg 89.76 Ib ft3 x 12 x 89.8 Ws -6.5 Effective submerged weight per foot of the pipelineplus internal contents lbs ft Lj 91ft Length of...
Safety
Each bidder should submit a copy of the company safety manual, including Operating procedures that comply with applicable regulations, including shoring of pits and excavations when required Emergency procedures that comply with applicable regulations for inadvertently boring into natural gas lines, live power cables, water mains, sewer lines, or fiberoptic cables Emergency evacuation plan in case of an injury The drilling unit must be equipped with an electrical strike safety package. The...
Unified Classification System for Soil Type
The type of soil at a crossing site should be classified using a standard classification system. The purpose of a soil-classification system is to provide the engineer with a method to predict the behavior of the soil for engineering projects. For a soil-classification system to be effective in the HDD industry, it must be widely used, simple, inexpensive, and based on parameters that impact the HDD process. The unified soil-classification system USCS satisfies these standards. It is described...
HDD DownHole Equipment
Unglamorous as down-hole equipment may be, these tools perform their vital functions underground and out of sight, and no drill rig can function without them. Bits and reamers, transmitter housings, swivels and pulling heads all are down-hole tools necessary to make HDD possible. Bits cut through soil to make pilot holes. The slant-face bits still used by most drillers making utility installations provide the steering ability that makes the HDD rigs directional. Reamers enlarge pilot holes to...
Axial Tensile Stress
The maximum tensile stress during pullback is the sum of the tensile stress due to the pullback force, including the hydrokinetic force, and the tensile stress resulting from the bending of the pipe. The average axial stress acting on the pipe cross-section at points 1, 2, 3, or 4 is given by Tx DR2 E D x 2 , -TT Equation 7-16 ox average outer-fiber axial tensile stress at corresponding point in psi Tx tensile force at corresponding point in foot-pounds D pipe outside diameter in inches DR pipe...
Drilling Fluid Collection and Disposal
The collection and handling of drilling fluids and inadvertent returns is perhaps one of the most debated topics in the HDD community in North America. On one side the industry realizes the need to keep drilling fluids out of streams, streets, and municipal sewer lines. On the other hand, tough new regulations in some states e.g., California present HDD contractors with escalating expenses. Owners need to adopt an approach that addresses environmental concerns while at the same time avoiding...
Resistance to External Collapse Pressure During Pullback Installation
The allowable external buckling-pressure equation, Equation 4-14, with the appropriate time-dependent modulus value can be used to calculate the pipe's resistance to the external pressure during pullback with proper reductions. The reduction occurs due to ovality and the hoop strain created by the pulling force. If the pipe is empty, the buoyant force will cause a reduction in the vertical diameter. The deflection fraction due to buoyancy can be calculated using Equation 4-13. This value can be...
Mud Motor Rock Bits
Increase width, length, and or angle for more aggressive steering May be modified by adding teeth, tapers, etc. to match conditions Small surface steering area abrasion and impact resistant cutters Refer to International Association of Drilling Contractors for numbering schemes Refer to International Association of Drilling Contractors for numbering schemes No moving parts Sealed Bearing Roller-cone Tungsten Carbide Inserts Sealed Bearing Roller-cone Drag Bit Polycrystal Diamond Compact PDC...
Torque and RPM Considerations
Torque and drill-pipe rotational speed RPM are the drill-rig characteristics that determine possible production rates. Torque and rotational speed are a measure of the drive-spindle horsepower, delivered through the drill string, available at the drill bit or reamer. This is not the case when auxiliary power is used, such as a down-hole mud motor. The basic equation for horsepower is HP spindle horsepower T spindle torque, foot-pounds RPM spindle speed As can be seen in the above equation,...
Pilot Hole
The first step in a HDD installation is to drill a carefully guided pilot hole that delivers the drill bit and bore head to the surface at the specified exit point. The bore is launched from the surface, and the pilot bore proceeds downward at an angle until the necessary depth is reached. A small-diameter drill string penetrates the ground at a prescribed entry point and the design entry angle, normally between 8 and 16 degrees. To help prevent the drill rod from deflecting upward or to the...
HDD Risk Identification
Potential risks that are a part of all HDD projects include a failure to complete the bore, safety of the public and workers, environmental issues, damage to surface structures, and striking other underground structures. Risk reduction is the attempt to identify potential risks during the planning and design phase so that they may be eliminated or reduced. A risk contingency plan is often used by the engineer and or contractor to help identify the major risks and develop general plans and...
Reaming
Once the pilot hole is successfully drilled, the hole is often enlarged to a suitable diameter for the product pipeline. For instance, if the pipeline to be installed is 8 inches in diameter, the hole may be enlarged to 12 inches or more. This is accomplished by reaming the hole to successively larger diameters. Generally the reamer is attached to the drill string on the bank opposite the drilling rig, rotated, and pulled pushed in some instances back through the pilot hole. Joints of drill...
HardRockMud Motor Bit
Hard-rock bits are used in ground conditions ranging from hard soil to hard rock with compressive strengths up to 40,000 psi or higher. When drilling in rock or hard soils, the drill bit cannot be pushed without rotation. In these soil conditions aggressive cutting bits and mud motors are used. Hard-rock or mud motor bits are classified as tri-cone bits with mill-tooth and tungsten-carbide inserts, drag bits, and polycrystal-diamond-compact PDC drag bits. For rock drilling positive-displacement...
Frictional Resistance
Pipe resistance to pullback in the bore hole depends primarily on the frictional force created between the pipe and the hole or the pipe and the ground surface in the entry area, the frictional drag between pipe and drilling slurry, the capstan effect at bends, and the weight of the pipe. Equation 7-4 gives the frictional resistance or required pulling force for pipe pulled in straight, level bores or across level ground Figure 7-2 . FP pulling force in pounds coefficient of friction between...
Average Radius of Curvature
The average radius of curvature for a pipe segment, such as point 1 to point 2 or point 3 to point 4 in Figure 7-1, may be estimated from the entry and exit angles and the depth of the bore by and the radius of curvature at any point along the bore path may be estimated by Ravg average radius of curvature along the bore-path segment in feet H depth of the bore beneath the surface in feet O bore entry and exit angle to the surface in radians degrees R local radius of curvature along the bore...
Pulling Back
The total volume, Vpua, in barrels of drilling fluid consumed not available for recirculation during pull back pipe installation is given by drilling fluid flow rate, barrels per minute drilled length, feet estimated pullback penetration rate, feet per minute pullback circulation loss factor Using the above equations, the total estimated volume of drilling fluid consumed Vconsumed is the sum of Vpiiothole, Vream, Vpuii, and the fluid system line fill. The fluid system line fill is the volume of...
ProductPipe Considerations
During the design process an evaluation of the product to be installed by HDD is critical. The design should evaluate the product pipe's suitability for the installation loads, corrosion conditions, pull-in installation, and intended function. In general, the pipe to be installed must be capable of being joined together continuously while maintaining sufficient strength to resist the high tensile stresses imposed during the pullback operation. The primary criterion governing the specification...
Operating Stresses
The operating stresses of concern include a combination of the longitudinal curvature stresses, external pressure stresses, and hoop and longitudinal stresses mentioned above. For operating stresses, the maximum working pressure of the pipeline is used to calculate the longitudinal and hoop stresses that will be imposed during service. After determining the individual and combined stresses, they are compared with the allowable stress limits for the product pipe. For example, ASME B31.8 provides...
Steel Product Pipe
Steel-pipeline properties such as wall thickness and material grade, as well as the bore path profiles, must be specified so the pipeline can be installed and operated without risk of damage. During HDD installation the pipeline is subjected to tension required to pull the pipe into the pilot hole and around curved sections. The tension comes from the drag due to the friction between pipe and bore hole and the fluid drag caused by pulling the pipe through the viscous drilling mud trapped in the...
Calculating the Pull Loads
The first step in calculating the estimated pulling loads is to develop the input data that will be used in the calculations. This data includes the product-pipe material properties, the drilling-fluid properties, and any code or design factors that are applicable. An example of the input data required for calculating estimated pulling loads is provided in Example 6-1 later in this chapter. Defining the Bore Path The next step is to define the bore path for the crossing. Figure 6-1 defines a...
Transmitter Housings
Bit location and data needed to guide the drill path are relayed to the drilling crew by a radio transmitter located behind the drill bit. While the transmitter itself isn't classified as a down-hole tool, the housing it's in is one of the most important down-hole components, protecting the tool from the stresses of drilling and allowing cooling fluid to flow around the transmitter. The newest radio-transmitter housings are made of more durable materials to resist cracking, and their designs...
General Information
Determining the loads and stresses that the product pipe will experience as a result of installation by HDD is an important process and a primary concern for the owners and engineers of the pipeline system. HDD contractors, on the other hand, are usually concerned about the loads and stresses on the drilling equipment. It is common for owners and engineers who are unfamiliar with HDD design and construction methods to rely solely on the advice of the contractor as to whether a crossing is...
Cable and PipePulling Devices
Cable grips are used for pulling cables and small-diameter pipe, usually 4 inches or less. Cable grips are attached to the outside of the pipe and can be taped or tied with clamps at the end to prevent them from pulling off. When using cable grips for pulling pipe, the normal practice is to use a solid insert that is at least twice as long as the inside diameter of the pipe in order to help prevent the pipe from collapsing. Duct pullers are also a very important part of pullback operation. The...
Percussive Drilling
One of the most common misconceptions about a percussive hammer is that it is not a proven method for rock drilling. Percussive hammers have been around for decades in the vertical industry. There are three basic categories rotary, percussive drifter, and down-the-hole percussive hammer. Rotary drill equipment was covered in the previous sections. Drifter percussive drills do not rely on high thrust or high torque for the cutting action they operate on the percussive energy that comes from a...
BorePath Geometry for Plastic Pipe
In addition to the bore-path-geometry methods discussed for steel pipe in Chapter 6, other methods from ASTM1 and plastic pipe organizations1 are often used for plastic-pipe crossings. These methods use an average radius of curvature for the pipe section from the entrance of the bore hole to the end of the curve. Figure 7-1 defines a typical bore-path profile used for plastic-pipe crossings. The values are assigned based on the profile required to successfully cross the obstacle while reaching...
Subsurface Conditions and Considerations
The decision to use the HDD method for a crossing should be based on an understanding of the HDD process and the crossing site's characteristics. The natural and man-made features in the area will dictate the design for the HDD crossing. After determining if the surface conditions are suitable for HDD construction, the next item to consider is the subsurface conditions. A vital element of many HDD design projects is a comprehensive geotechnical survey to identify soil formations at the...
Noise
Noise is often an area of concern in congested urban areas. Many local areas do not have noise ordinances that establish limits such as maximum decibel levels. In fact, there does not seem to be any consensus on what level of noise is a problem. If the regulatory agency has noise-control provisions, the contractor may use the manufacturer's specifications for the equipment and or measure noise levels at various distances. Based on the data, noise-abatement equipment can be used as necessary to...
Geotechnical Investigation
The information from the geotechnical survey is used to select the crossing route, drilling tools, procedures, and the drill-path design. The level of effort required for the geotechnical investigation depends on several factors, such as the pipe diameter, bore length, and the nature of the HDD crossing. For many HDD projects, especially in municipal areas, the subsurface investigation consists primarily of research of existing geotechnical data. Due to the costs and the congested nature of...
Pullback Loads
HDD drill rigs can exert extensive pull forces. Most of the force is applied to the cutting face of the reamer. As discussed in Chapter 6, it is a difficult task to estimate what portion of the total pullback force is being transmitted to the product pipeline. The pulling force, which overcomes the combined frictional drag, capstan effect, and hydrokinetic drag, is applied to the first joint of plastic pipe. The axial tensile stress intensifies over the length of the pull. The duration of the...
Disadvantages
No disturbance in water body or wetland. Ground disturbance of drilling and target areas. Fractures in the subsurface may release drilling fluids into the water body. Greatly reduces the clean-up and reclamation efforts and costs. Largely dependent upon the subsurface conditions. Specialized equipment and crews required. Limits on the stress radius of the pipe to be installed. Another factor in the increased popularity of HDD for municipal applications is the acceptance of HDPE pipe for water...
SMYS fl fs
F maximum allowable pull force, pounds R design radius of curvature, feet E modulus of elasticity, psi A cross-sectional pipe area, inches2 D pipe outside diameter, inches SMYS specified minimum yield strength of the steel, psi fl maximum load factor fs safety factor TABLE 4-1 Typical Steel Pipe Specification for HDD Steel pipe shall conform to API 5L X52 specifications. The pipe shall be seamless or electric resistance welded ERW steel pipe as specified in ASME B31.8. Butt-weld fittings shall...
Surfactants
Surfactants, or soaps, are wetting agents that are used to break clay water bonds and disperse clay particles to stop or break up clumps. Surfactants are usually used in sticky clays. TABLE 5-3 Applications of Bentonite-Based Drilling Fluids Courtesy of DCCA Bore Gel Specially blended system using high yielding Wyoming sodium bentonite. When mixed with fresh water, develops an easy to pump slurry with desirable properties for HDD drilling Quick-Gel Viscosifier and gallant. Easy to mix in fresh...